Process for producing image using laminated oriented cover film

ABSTRACT

A process for producing an image which comprises the steps of: 
     (1) applying to the surface of a substrate the surface of a photosensitive layer, the other surface of the photosensitive layer being adhered to a substantially transparent film support which is soluble or dispersible in a developer consisting essentially of a liquid capable of substantially dissolving or dispersing therein the areas of the layer other than those having a polymeric image produced by imagewise exposure in the step (2) below; 
     (2) exposing the photosensitive layer, imagewise, to actinic radiation to form a polymeric image in the layer; and 
     (3) washing away with the developer the film support and the areas of the layer other than those having the polymeric image to form an image of a polymeric material on the substrate. The photosensitive element having on its one side the above-mentioned specific film support and the process have a variety of applications and are useful for producing photoresists which are advantageously used for making printed circuit boards.

This invention relates to a photosensitive element, a process forproducing an image using the photosensitive element and applicationsthereof. More particularly, the invention relates to a photosensitiveelement comprising a photosensitive layer and a support which is solubleor dispersible in a developer consisting essentially of a liquid capableof substantially dissolving or dispersing therein the areas of the layerother than those having a polymeric image produced by imagewise exposureand is substantially transparent to actinic rays, and also relates to aprocess for producing an image using this photosensitive element. Theelement and process of this invention have a variety of applications,but may be employed for producing photoresists with great advantages.

Various processes and elements have been proposed for producingphotoresists which are useful for the production of printed circuitboards. For example, as a first instance of the conventional processesfor making photoresists, it is known to directly coat a photosensitiveliquid composition onto a substrate, dry the composition, image-wiseexpose the layer of the composition to actinic radiation and develop thelayer with a liquid developer. As a second instance of the conventionalprocesses, it is also known to use a photosensitive element comprising aflexible support film, a flexible photosensitive layer having adherenceto a substrate and laminated onto the flexible support film and aprotective film covering the other surface of the photosensitive layerto prevent blocking at the winding step and adhesion of dusts duringhandling. In the second instance, the production of photoresists aredone by the steps of stripping the protective film, applying thephotosensitive layer of the element to the substrate, exposing thephotosensitive layer, imagewise, to actinic radiation, stripping thesupport film either before or after imagewise exposure and developingthe layer with a liquid developer (see, for example, U.S. Pat. No.3,469,982). In the former case, the users purchase the photosensitiveliquid composition as such and coat it onto the substrate. Accordingly,the users are required to have the skill in the technique of uniformlycoating the liquid composition onto the substrate. In the latter case,although there is such an advantage that the skill required for theformer case is not needed because the provision of the photosensitivelayer on the substrate is easily effected only by the steps of strippingthe protective film and subsequently applying the photosensitive layeronto the substrate, some difficulties are still encountered.Illustratively stated, in the photoresist element employed in the lattercase, the support film for bearing the photosensitive layer must haveflexibility. In addition, it is indispensable that the adhesion betweenthe substrate and the photosensitive layer should be larger than theadhesion between the film support and the photosensitive layer.

When the photoresist element to be employed in the above-mentionedsecond instance of the conventional processes is employed for theproduction of a printed circuit board, the protective film is strippedand the photosensitive layer is then applied to a substrate forproducing thereon a permanent image, such as a copper-clad epoxy resinplate. If the film support is opaque, the film support is then strippedand the photosensitive layer is exposed imagewise to actinic radiation.If the film support is transparent, the photosensitive layer may beexposed imagewise to actinic radiation either before or after strippingof the film support. In either case, the film support is necessarilystripped prior to development. Then, the non-imaged areas of thephotosensitive layer are dissolved away using a liquid developer to forma resist image on the surface of the substrate. Thereafter, etching iseffected to obtain an intended printed circuit board.

At present, a polyethylene terephthalate film is most popularly used asthe film support because it has a high nerve and a good evenness. Sincethis film has polar groups in the molecular structure, it has aconsiderable adhesion to the photosensitive layer. In case a resist filmcomprising such a film support and a photosensitive layer is laminatedonto a substrate such as a copper-clad epoxy resin plate, the substrateand/or the resist film is heated and pressure lamination is theneffected so as to attain good adherence between the photosensitive layerand the substrate. If heating and/or pressure application is not uniformand/or the substrate is warped, uniform adhesion between the substrateand photosensitive layer cannot be attained, and therefore, when thefilm support is stripped, there is often caused such a trouble that partof the photosensitive layer remains attached to the film support and theformer is removed together with the latter. It is not practicallyacceptable to subject the substrate having thereon such an incompletelamination to the subsequent step such as development. Further, if thetemperature at the heat-lamination step is low, the adhesion between thesubstrate and the photosensitive layer is sometimes insufficient,leading to such a trouble that when the film support is stripped, thephotosensitive layer is peeled off together with the film support. Thisundesirable trouble takes place when the adhesion between the filmsupport and the photosensitive layer is larger than the adhesion betweenthe substrate and the photosensitive layer.

Reduction of the thickness of the photosensitive layer is an effectivemeans for improving the resolution of a resist image produced therefrom.However, if the thickness of the photosensitive layer is reduced, theabsolute value of cohesion of the layer is lowered, and hence there iscaused occurrence of such an undesirable phenomenon that thephotosensitive layer is destroyed when the film support is stripped.Therefore, there is inevitably limitation with respect to the reductionof the thickness of the photosensitive layer.

The foregoing defects and disadvantages are inevitably involved in theconventional processes using liquid-development type photosensitiveelements for producing photoresists.

It is therefore a principal object of this invention to provide a newand improved process for producing an image which is particularly usefulas a photoresist. Another object is to provide a rapid and practicalprocess for producing a durable photoresist useful for the production ofa printed circuit board. It is still another object of this invention toprovide an improved and practical method for the production of a printedcircuit board. A further object is to provide a preformed photosensitiveresist element useful for practicing the processes as described above.

We made intensive researches with a view to obviating the defects anddisadvantages involved in the conventional techniques. As a result, itwas found that the purpose of our researches can be simply attained bythe use of a photosensitive element comprising a layer made of aphotosensitive composition and a film support made of a transparentmaterial such as a transparent polymeric material and laminated on thesurface of the photosensitive composition layer which support is solubleor dispersible in a developer consisting essentially of a liquid capableof substantially dissolving or dispersing therein the areas of thephotosensitive composition layer other than those having a polymericimage produced by imagewise exposure. In order to produce a resist imageon a substrate by the use of the above-mentioned photosensitive element,there is employed a process comprising applying the photosensitive layerof the element onto the substrate and exposing the photosensitive layer,imagewise, to actinic rays to form a polymeric image, directly followedby development without stripping from the layer the film support. In theprocess, the film support is advantageously washed away together withthe areas of the photosensitive composition layer other than thosehaving the polymeric image by using the developer.

Essentially, in accordance with the present invention, there is provideda process for producing an image, which comprises the steps of:

(1) applying to the surface of a substrate the surface of aphotosensitive composition layer having adherence to the substrate,while the other surface of the photosensitive composition layer hasadhered to a substantially transparent film support which is soluble ordispersible in a developer consisting essentially of a liquid capable ofsubstantially dissolving or dispersing therein the areas of the layerother than those having a polymeric image produced by imagewise exposurein the step (2) below and capable of transmitting actinic rays, theapplication of the surface of the photosensitive composition layer tothe surface of the substrate being effected after stripping of aprotective film in case the protective film has been provided on thesurface of the photosensitive composition layer remote from the filmsupport;

(2) exposing the photosensitive composition layer, imagewise, to actinicradiation to form a polymeric image in the layer; and

(3) washing away with the developer the film support and the areas ofthe layer other than those having the polymeric image to form an imageof a polymeric material on the substrate.

Either a photopolymerizable composition or a photodegradable compositionmay be employed as the photosensitive composition to be used in thisinvention. The photopolymerizable composition is used for formation of anegative image while the photodegradable composition is used forformation of a positive image. In general, negative workingphotosensitive compositions are employed in most cases. Accordingly, thefollowing description will be made mainly with reference to anembodiment in which a photopolymerizable composition is used as thephotosensitive composition.

A process for producing an image according to this invention ispracticed, for example, as follows. If a photosensitive elementcomprising a photopolymerizable layer made of a photopolymerizablecomposition and capable of being dissolved or dispersed in a liquiddeveloper and a film support attached to one surface of the layer isprovided on the other surface of the photopolymerizable layer with aprotective film, the protective film is firstly stripped. The surface ofa photopolymerizable layer of the photosensitive element is laminatedand attached to the surface of a substrate such as a copper-clad plate.Subsequently, the photopolymerizable layer is imagewise exposed toactinic radiation to form a polymeric image by photopolymerization ofthe photopolymerizable composition. The film support and the unexposedareas of the layer are then washed away with the liquid developer toform an image of a polymeric material on the surface of the substrate.

In case the so formed image of the polymeric material is used as aresist image for the production of a printed circuit board, thesubsequent procedures are as follows. The resist image bearing substrateis dipped in an etching solution containing ferric chloride or the like,whereby the bared surface portions of the substrate which are made ofcopper or the like and unprotected by the resist image are etched away.The so treated substrate is picked up from the etching solution, and theresist image is removed to obtain a desired printed circuit board.

At the step of lamination of a photosensitive layer to a substrate, thetemperature of the surface of the substrate and/or the surface of thephotosensitive layer remote from a film support and the pressure to beapplied between the substrate and the photosensitive layer may be varieddepending on the kinds of the substrate and the photosensitive layer.But the temperature is usually about 0° to about 160° C., preferablyabout 10° to about 120° C. and the pressure is usually about 0.1 toabout 20 kg/cm².G, preferably about 0.5 to about 5.0 kg/cm².G.

The photopolymerizable type photosensitive elements useful for producingphotoresists comprises, as essential elements, a transparent filmsupport and a photopolymerizable layer including an organic binderselected from polymeric materials capable of being dissolved ordispersed in an organic solvent to be used as the developer, andoptionally it further comprises a protective film.

In this invention, a transparent film support capable of being dissolvedor dispersed in a developer may be a film having either no orientationor orientation. In general, a support film having orientation, such as amonoaxially or biaxially oriented film, is preferred. As the materialsof the support film, there can be mentioned various kinds of polymers,for example, methyl methacrylate homopolymer and copolymers with amonomer or monomers such as methacrylic acid, acrylic acid, methylacrylate, butyl acrylate, etc., styrene homopolymer and copolymers witha monomer or monomers such as acrylonitrile and/or butadiene, polyvinylchloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers,polyvinyl alcohol, polyvinyl pyrrolidone, polycarbonates, chlorinatedpolyolefins such as chlorinated polyethylene and chlorinatedpolypropylene, cellulose derivatives such as cellulose diacetate,cellulose triacetate and cellulose acetate butyrate, and mixturesthereof. The viscosity average molecular weight of the polymericmaterial for the support film is not critical and any polymeric materialmay be used so far as it can be removed by dissolution or dispersioninto a liquid developer at the step of development. The viscosityaverage molecular weight may be 5,000 to 1,000,000.

As described hereinbefore, the liquid developer to be used in thisinvention must be capable of dissolving or dispersing therein both ofthe unexposed areas of the photopolymerizable layer and the filmsupport. As specific examples of an organic solvent as the developer,there can be mentioned ketones such as acetone and methyl ethyl ketone;esters such as methyl formate, methyl acetate, ethyl acetate and amylacetates; chlorinated hydrocarbons such as chloroform,trichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane andmethylene chloride; aromatic hydrocarbons such as benzene, toluene andxylene; alicyclic hydrocarbons such as cyclohexane; alcohols such asmethanol, ethanol and isopropanol; cellosolves such as methylcellosolve; and tetrahydrofuran. These solvents may be used either aloneor in mixture.

As an organic polymer binder to be used in a photopolymerizable layer ofthe photosensitive element, there can be mentioned, for example, methylmethacrylate homopolymer and copolymers with a monomer or monomers suchas methacrylic acid, acrylic acid, methyl acrylate, butyl acrylate,etc., styrene-acrylonitrile copolymers, chlorinated polyolefines such aschlorinated polyethylene and chlorinated polypropylene, polyvinylbutyral and mixtures thereof. Of these organic polymer binders, methylmethacrylate homopolymer and copolymers are especially preferred fromthe viewpoint of the compatibility with a photopolymerizable monomer tobe used for the photopolymerizable layer and/or the affinity with theliquid developer such as mentioned above. The viscosity averagemolecular weight of the organic polymer binder is not critical and anypolymer binder may be used so far as it can be removed by dissolution ordispersion into a liquid developer at the step of development. Theviscosity average molecular weight may be 5,000 to 1,000,000.

In general, an appropriate liquid developer is chosen according to thekinds of the organic polymer binder for the photopolymerizable layer andthe polymeric material for the film support. For example, when thebinder and the support film are of acrylic polymers, e.g., polymethylmethacrylate, ketones and/or chlorinated hydrocarbons are used as theliquid developer, while ketones are used for vinyl chloride typepolymers and ketones and/or esters are used for cellulose derivatives.When the kind of the organic binder is different from that of thesupport film, a common solvent for both of them or an appropriatemixture of solvents is chosen and employed as the liquid developer.

In this invention, development may be effected by dissolution of theunexposed areas of the photopolymerizable layer and the film support.Alternatively, development may be accomplished by swelling of the layerand/or the support and subsequent dispersion and removal thereof. Forexample, when polyvinyl butyral is used as the binder of thephotopolymerizable layer and polyvinyl alcohol or polyvinyl pyrrolidoneis used as the support, a liquid mixture of water and ethanol may beused as the liquid developer.

The photopolymerizable layer may comprise a photopolymerizable monomer,an organic polymer binder such as mentioned above, and a sensitizingagent such as a photopolymerization initiator. Ethylenically unsaturatedcompounds, especially acrylic polyfunctional monomers, are suitablyemployed as the photopolymerizable monomer. As the photopolymerizablemonomer, those having at least 2 unsaturated bonds in their molecule arepreferred because they provide crosslinkages by photopolymerization whenexposed to actinic radiation. As acrylic monomers having 2 unsaturatedbonds, there can be mentioned, for example, diacrylates such aspolyethylene glycol diacrylate and polypropylene glycol diacrylate, anddimethacrylates such as polyethylene glycol dimethacrylate andpolypropylene glycol dimethacrylate, and as acrylic monomers having 3unsaturated bonds, there can be mentioned, for example, triacrylatessuch as pentaerythritol triacrylate and trimethylolpropane triacrylateand trimethacrylates such as pentaerythritol trimethacrylate andtrimethylolpropane trimethacrylate. The viscosity average molecularweight of polyethylene glycol diacrylate, polypropylene glycoldiacrylate, polyethylene glycol dimethacrylate and polypropylene glycoldimethacrylate as mentioned above is not critical but is usually up to10,000, preferably up to 5,000. Other ethylenically unsaturatedcompounds that can be used as the photopolymerizable monomer are, forexample, those as disclosed in U.S. Pat. No. 3,469,982, polyvinylcinnamate and polyacrylamide. These monomers may be used either alone orin mixture. The ratio of the amount of the photopolymerizable monomer tothe amount of the organic polymer binder may be chosen within a broadrange according to the kinds of the monomer and the binder so far as adesired image can be obtained from the photopolymerizable layer preparedtherefrom. In general, the photopolymerizable monomer is used in anamount of 10 to 500 parts by weight, preferably 20 to 200 parts byweight, per 100 parts by weight of the binder.

The kind of a photopolymerization initiator to be used as thesensitizing agent is not particularly critical in this invention, andany of known photopolymerization initiators can be used. Specificexamples of such photopolymerization initiators include carbonylcompounds such as benzoin, benzoin C₁ -C₄ alkyl ethers, benzophenone,anthraquinone, 2-methylanthraquinone, 2-tert-butylanthraquinone,9,10-phenanthrenequinone, diacetyl and benzil; peroxides such ashydrogen peroxide, di-tert-butyl peroxide, benzoyl peroxide and methylethyl ketone peroxide; organic sulfur-containing compounds such asdi-n-butyl disulfide; 2-mercaptobenzothiazole, 2-mercaptobenzoxazole,2-mercaptobenzimidazole, thiophenol, thiocresol,carboxymethyl-N,N-dimethyldithiocarbamate and ethyltrichloromethanesulfonate; redox initiators such as ferrous ion-peroxidesuch as hydrogen peroxide, ferric ion-peroxide such as hydrogen peroxideand ferrous ion-persulfate ion; photoreducible dyes such as RoseBengale, Erythrocin, Eosine, acriflavine and Thionine; halogen compoundssuch as chloromethylnaphthyl chlorides, phenacyl chloride,chloroacetone, β-naphthalenesulfonyl chloride and xylenesulfonylchlorides; and azo or diazo compounds such asα,α'-azobisisobutyronitrile, 2-azobis-2-methylbutyronitrile and adiazonium salt, e.g. a diazonium chloride, of p-aminodiphenylamine. Inthe above-mentioned redox initiators, the source of ferrous ion may beferrous chloride, the source of ferric ion may be ferric chloride andthe source of persulfate ion may be ammonium persulfate. The ratio ofthe amount of the photopolymerization initiator to the amount of thephotopolymerizable monomer can be chosen within a broad range accordingto the kinds of the monomer and the photopolymerization initiator so faras a desired image can be obtained. In general, it is preferred that theamount of the photopolymerization initiator be 0.1 to 20 parts byweight, especially 1 to 10 parts by weight, per 100 parts by weight ofthe monomer.

In this invention, it is noted that the photopolymerizable layer may beof a multi-layer type in which the respective layers have successivelyincreased concentrations of the photopolymerization initiator withincrease in their distances from the film support. In the case of such amulti-layer type photopolymerizable layer, insufficient exposure toactinic radiation in the portions of the layer remote from the filmsupport is compensated by the increased amount of the initiator toprovide substantially uniform photopolymerization with respect to thevertical direction of the photopolymerizable layer. The substantiallyuniformly photopolymerized image gives, after development thereof, animage resist having substantially vertical lateral faces. Usually, aphotopolymerizable layer having two layers differing in theconcentration of the initiator is provided for attaining theabove-mentioned purpose. In this case, the concentration of thephotopolymerization initiator in the layer on the side remote from thefilm support is suitably 1.5 to 10 times that in the layer on the sideof the film support.

The photopolymerizable layer may include a polymerization inhibitor. Asthe polymerization inhibitor, there can be used, for example,p-methoxyphenol, hydroquinone, hydroquinones substituted with an alkylgroup such as methyl or ethyl or an aryl group such as phenyl,t-butylcatechol, pyrogallol, cuprous chloride, phenothiazine, chloranil,naphthylamines, β-naphthol, 2,6-di-t-butyl-p-cresol, pyridine,nitrobenzene, dinitrobenzenes, p-toluidine, Methylene Blue and coppersalts of organic acids such as acetic acid. The amount of thepolymerization inhibitor may vary according to the kinds of thephotopolymerizable monomer and the polymerization inhibitor. In general,however, the polymerization inhibitor is used in an amount of 0.01 to 5parts by weight per 100 parts by weight of the photopolymerizablemonomer.

In connection with the use of a polymerization inhibitor, it is notedthat the photopolymerizable layer may be of another multi-layer type inwhich the respective layers have successively decreased concentrationsof the polymerization inhibitor with increase in their distances fromthe film support. In the case of such a multi-layer typephotopolymerizable layer, substantially uniform photopolymerization withrespect to the vertical direction of the photopolymerizable layer isattained by exposure of the layer to actinic radiation. Thesubstantially uniformly photopolymerized image gives, after developmentthereof, an image resist having substantially vertical lateral faces.Usually, for attaining the above-mentioned purpose, there is provided aphotopolymerizable layer having two layers differing in theconcentration of the inhibitor. In this case, the concentration of thepolymerization inhibitor in the layer on the side remote from the filmsupport is suitably 0.01 to 0.5 time that in the layer on the side ofthe film support.

In order to increase the visibility of the image, a coloring agent maybe incorporated into the photopolymerizable layer. Any of coloringagents as used commonly in this field may be employed. For example,there can be used titanium dioxide, carbon black, Crystal Violet, azopigments, iron oxides, phthalocyanine pigments, Methylene Blue,Rhodamine B, Fuchsine, Auramines, azo dyes and anthraquinone dyes. Incase a pigment is used as the coloring agent, it is incorporated in anamount of 0.1 to 25 parts by weight, preferably 0.1 to 5 parts byweight, per 100 parts by weight of the sum of the binder and themonomer. In case a dye is used as the coloring agent, it is incorporatedin an amount of 0.01 to 10 parts by weight per 100 parts by weight ofthe sum of the binder and the monomer.

A nitrogen-containing heterocyclic compound may be incorporated into thephotopolymerizable layer according to need. Any of nitrogen-containingheterocyclic compounds as used commonly in this field can be used. Forexample, there may be used benzimidazole, 2-aminobenzimidazole,5-nitrobenzimidazole, 5-methylbenzimidazole, benzotriazole,1-chlorobenzotriazole and 2-aminobenzothiazole. By incorporation of sucha nitrogen-containing heterocyclic compound into the photopolymerizablelayer, the tack of the photopolymerizable layer to a metal-cladsubstrate or a metal substrate can be improved. In general, it ispreferred that the nitrogen-containing heterocyclic compound beincorporated in an amount of 0.1 to 10 parts by weight, especially 0.5to 5 parts by weight, per 100 parts by weight of the sum of the binderand the photopolymerizable monomer. Alternatively or additionally, anadhesive may be applied onto the substrate for improving the adherencebetween the photopolymerizable layer and the substrate.

Further, a plasticizer may be incorporated into the photopolymerizablelayer according to need. Any of plasticizers as used commonly in thisfield can be used in this invention. For example, there can be usedphthalic acid esters such as dimethyl phthalate, diethyl phthalate,dibutyl phthalate and dioctyl phthalate; glycol esters such as dimethylglycol phthalate and ethyl phthalyl ethyl glycolate; phosphoric acidesters such as tricresyl phosphate and triphenyl phosphate; and estersof aliphatic dibasic acids such as diisobutyl adipate, dioctyl adipateand dimethyl sebacate. The plasticizer is used in an amount of 0.1 to 30parts by weight, preferably 2 to 10 parts by weight, per 100 parts byweight of the sum of the organic polymer binder and thephotopolymerizable monomer.

As described before, positive working photodegradable compositions canbe used as another type photosensitive composition in the process ofproducing an image according to this invention. As an organic polymerbinder to be used for the positive working photosensitive layer, therecan be mentioned, for example, methyl methacrylate copolymers withacrylic acid and/or methacrylic acid, novolak resins, cellulosederivatives such as cellulose acetate succinate, and mixtures thereof.With respect to the film support, a film made of an aqueoussolvent-soluble polymer such as polyvinyl alcohol, polyvinylpyrrolidone, cellulose acetate succinate or the like may advantageouslybe used as the film support. The term "aqueous solvent" as used hereinincludes water alone and an aqueous solution of an acid or alkali. Asthe photodegradable compositions, there may advantageously be employedthose containing an o-quinone diazide because they have an excellentresolution. When the o-quinone diazide type photosensitive compositionis employed, an aqueous alkali solution may be used as the liquiddeveloper.

A photosensitive element to be used for producing an image according tothis invention is easily prepared, for example, as follows. A solutionof a photosensitive composition is coated onto a plate or film havingrelease properties to form a photosensitive layer and the photosensitivelayer is transferred to a support film to give a photosensitive elementhaving no protective film. In case a support film has resistance tosolvent attack of a solution of a photosensitive composition, thesolution may be directly coated onto the support film to form aphotosensitive element. In the case of a photosensitive element having aprotective film, a solution of a photosensitive composition is coatedonto a protective film to form a photosensitive layer and thephotosensitive layer with the protective film is laminated onto asupport film. Instead of lamination, a polymer solution or emulsion maybe coated onto the photosensitive layer to form a support layer. Such asupport layer is, of course, included in the definition of the term"film support" or "support film" as used herein.

The photosensitive element for producing an image according to thisinvention comprises an unoriented or oriented transparent film supportmade preferably of a polymeric material selected from the polymersmentioned hereinbefore and a photosensitive layer. An appropriate liquiddeveloper capable of dissolving or dispersing therein both of the filmsupport and the non-imaged portions of the layer is chosen from amongthe aforementioned solvents and is used for development. However, itshould be noted that advantageously employable liquid developers are notlimited to those exemplified hereinbefore.

The term "liquid developer" as used herein is intended to mean a liquidcapable of removing the film support and the non-imaged areas of thelayer to form an image. Accordingly, even if a liquid is incapable ofdissolving away the film support and/or the non-imaged areas of thelayer, it can be used as a developer in case it is capable of removing,by any means, the film support and the non-imaged areas of the layer byany treatment with the liquid developer.

The thickness of the photosensitive layer that is used in this inventionis preferably 0.1 to 1,000μ, more preferably 1 to 100μ. The thinner thephotosensitive layer, the more the resolution is improved.

The thickness of the unoriented or oriented transparent film support ispreferably 5 to 100μ, more preferably 10 to 50μ. This is so because thetransparent film support must impart to the photosensitive element astrength sufficient to resist the stripping of the protective film andresist the lamination to the substrate so as to avoid deformation of thephotosensitive element, and also because the time required fordevelopment can be shortened as the transparent film support is thin.The oriented film support may be obtained by a customary process, forexample, stretching-orientation or rolling-orientation. A biaxiallyoriented film support is most suitable employed as the film support.

In general, an oriented transparent support is thin and neverthelessimparts a sufficient nerve to a photosensitive element. Further, in thiscase, the dissolution of the film support is facilitated by the residualinternal stress due to molecular orientation and therefore, thedevelopment time can be shortened. Moreover, by the use of a thin filmsupport, the range of scattering of actinic rays in the film can benarrowed to improve the resolution of the image. Thus, various practicaladvantages can be attained by the use of an oriented transparent filmsupport.

An appropriate protective film may be chosen from among known materials.As the protective film, there can be mentioned, for example, apolyethylene terephthalate film, a polypropylene film, a polyethylenefilm, a cellulose triacetate film, a cellulose diacetate film, apolyamide film, a polytetrafluoroethylene film, a paper, apolyethylene-laminated paper and a polypropylene-laminated paper. Thethickness of the protective film is 8 to 80μ, preferably 10 to 30μ.

As the substrate for producing thereon an image, there can be mentioned,for example, a laminate board with its surface or surfaces etchable byan etching liquid, a metal plate such as a copper, aluminum, iron,brass, silver, gold or stainless steel plate, a glass plate and a stoneplate. The laminate boards with its surface or surfaces etchable, e.g.copper-clad substrate and aluminum-clad substrate, are useful forproducing a printed circuit board according to the process of thepresent invention.

As the light source for exposure to actinic radiation, there can beused, for example, a high pressure mercury lamp, a super high pressuremercury lamp, a low pressure mercury lamp, a xenon lamp, a carbon arclamp and a fluorescent lamp. Besides actinic rays from these lightsources, there may be used X-rays, laser rays and electron rays forimagewise exposure.

As will be apparent from the foregoing illustration, the troublesomestep of stripping the film support before or after exposure can beomitted according to this invention. Since the film support need not bestripped, the thickness of the photosensitive layer can be remarkablyreduced without the cohesion of the photosensitive layer being takeninto account. As a result, the resolution of the image can be remarkablyimproved. Further, when the photosensitive element for practicing theprocess of this invention is laminated to the substrate with heating,since the film support need not be stripped, the temperature need not beelevated to such a high level as adopted in the conventional technique.Further, even if the adhesion between the photosensitive layer and thesubstrate is small, good results are obtained if only the adhesionbetween the image formed by the development and the substrate issufficient to resist the subsequent treatment such as etching.Therefore, handling of the photosensitive element can be remarkablysimplified and facilitated in this invention. Still further, nonuniformadhesion between the photosensitive layer and the substrate owing tononuniform heating or pressing is no longer a problem in this invention.

The photosensitive element and the process for producing an imageaccording to this invention may advantageously be utilized for theproduction of printed circuit boards, but the application field of thisinvention is not limited to the production of printed circuit boards.For example, the process of this invention is effectively applicable tochemical milling or processing of semiconductors. The process can alsobe applied to the production of photorelieves such as those for aprinting plate, a name plate, decorative articles and the like.

The process for producing an image according to this invention can beapplied advantageously to the various conventional methods for producingprinted circuit boards by means of photoresists. Two distinct methods ofthe manufacture of printed circuit boards for use in electrical orelectronic equipments have, in general, been proposed in the prior art.One is called the "subtractive" method, and the other method is calledthe "additive" method. The "subtractive" method utilizing a photographicreproduction process consists, in general, in clothing one or both sidesof an insulating substrate with a conductive metal foil, covering theconductive metal-clad substrate with a photosensitive material layer,exposing the photosensitive layer to actinic radiation through a patternmask to form a latent image of the desired circuit and subjecting theimage-bearing substrate to development using a solvent capable ofremoving the non-imaged portions of the photosensitive material layerthereby to form a photoresist having a positive image of the desiredcircuit, followed by etching away of the metal foil in the areasunprotected by the photoresist to form the circuit conductor. When thesubstrate has on its both sides conductive metal layers and is providedwith through-holes, following etching, the entire surfaces of both sidesare covered, except portions corresponding to the through-holes, with aresist and the inner wall surfaces of the through-holes are plated withan electroless deposit of a conductive metal, optionally followed byelectro-deposition of a conductive metal on said electroless deposit(see, for example, German Offenlegungsschrift No. 24 27 610). Analternative to the "subtractive" method has been proposed heretofore,and is known as the "additive" method of manufacturing printed circuitboards. The "additive" method utilizing a photographic reproductionprocess consists, in general, in covering a bare substrate free of anyconductive metal foil with a photosensitive material layer, exposing thephotosensitive layer to actinic radiation through a pattern mask to forma latent negative image of the desired circuit and subjecting theimage-bearing substrate to development using a solvent capable ofremoving the non-imaged portions of the photosensitive material layerthereby to form a photoresist having a negative image of the desiredcircuit, followed by electroless deposition of a conductive metal ontothe areas unprotected by the photoresist, optionally further followed byelectro-deposition of a conductive metal thereonto, to form theconductor portions of the circuit. As an improvement of the "additive"method, there is known a method which involves the steps of punching abare substrate to provide necessary through-holes, plating an initialthin deposit of a conductive metal over the entire surface using anelectroless metal plating bath, then applying and developing aphotoresist to form a negative image of the desired circuit, followed byadditional metal plating by electro-deposition to build up the conductorportions of the circuit to a desired thickness, whereupon thephotoresist is removed from the non-circuit portions and the inital thinelectroless metal deposit is etched away therefrom. In any of themethods in which an electroless plating procedure is involved, thecatalyst for electroless plating is generally applied on the surface tobe plated or incorporated in the substrate itself.

As is easily understood to those skilled in the art, the process forproducing an image and the photosensitive element according to thepresent invention can be advantageously utilized for formation of thephotoresists functioning as the etching-resist and the plating-resist inthe above-mentioned "subtractive" method and "additive" method,respectively.

Furthermore, it is noted that as the modification of the above-mentioned"subtractive" method it is known to provide printed circuit boards ofthe type in which the substrate has on its both sides conductor circuitsand the conductor circuits formed on the opposite sides have electricalconnection therebetween through conductive metal layers formed on theinner wall surfaces of the through-holes of the substrate. The presentprocess for producing an image is applicable, with great advantages,especially to the manufacture of printed circuit boards of the type asmentioned above. In the conventional method for the production ofprinted circuit boards of this type, the printed circuit is formed bythe method comprising forming a resist, by using an etching-resistantmetal or ink having a masking capacity, on both surfaces of a conductivemetal-clad substrate and the inner wall surfaces of the through-holesformed in the substrate, said inner wall surfaces having thereonrespective conductive metal layers, and subjecting the resultingresist-bearing substrate to etching whereby predetermined,resist-unprotected areas of both surfaces of the metal-clad substrateare etched away. In this conventional method, the resist can be easilyformed on the surfaces of the substrate, but it is difficult to form aresist securely on the inner wall surfaces of the through-holes.Therefore, there is a tendency that the conductive metal formed on theinner wall surfaces of the through-holes is also etched, thus causingthe thickness of the conductive metal layer to be reduced in the etchedportions of the inner wall surfaces of the through-holes. As a result,the resistance is increased in these portions, leading to lowering ofthe performance of the printed circuit board.

As a means for overcomging the foregoing defects, there has recentlybeen proposed an improved method for forming printed circuit boards froma conductive metal-clad substrate having through-holes with theirrespective inner wall surfaces covered with conductive metal layers. Theimproved method consists in covering, with photosensitive layers, thesurfaces of both sides of the metal-clad substrate including bothopenings of each of the through-holes thereby to close the openings ofthe through-holes, so that the conductive metal layer on the inner wallsurface of each of the through-holes is protected from etching in thesubsequent step for forming the circuit conductors by etching (see, forexample, Japanese Patent Application Publication No. 3746/1971). In thisimproved method, for covering the surfaces of both sides of themetal-clad substrate with the photosensitive layers, there mayadvantageously be employed a photosensitive element comprising areleasing support such as a release paper and a photosensitive resinlayer formed on said support and optionally a protective film providedon the surface of said layer remote from the releasing support. Examplesof such a photosensitive element include Riston (registered trademark ofa product manufactured and sold by Du Pont Company, U.S.A.) and Laminar(registered trademark of a product manufactured and sold byThiokol/Dynachem Corp., U.S.A.). As described, Japanese PatentApplication Publication No. 3746/1971 discloses a method which comprisesapplying one side of a photosensitive resin layer having on its otherside a releasing support onto the surfaces of both sides of aninsulating substrate having thereon conductive metal layers such as thincopper layers and having through-holes thereby to effect closure of atleast both openings of the through-holes; in either order, imagewiseexposing the photosensitive resin layers on both sides of the substrateto actinic radiation to form predetermined insolubilizable patternimages covering and closing at least both openings of each of thethrough-holes and removing the releasing supports from thephotosensitive resin layers, followed by development; and etching theconductive metal layers in the areas other than the areas of said imagesas masking resists. In practicing this process, the releasing supportmust be removed from the photosensitive resin layer before the imagewiseexposure if the releasing support is opaque, or before or after theimagewise exposure if the releasing support is transparent. In general,a photosensitive resin having a high tack is used for the photosensitiveresin layer so as to attain a good adhesion between the photosensitiveresin layer and the conductive metal layer, and in addition, when thephotosensitive resin layer is laminated to the conductive metal layer,lamination is effected under application of pressure so as to securegood adherence. Accordingly, it is considerably difficult to remove thereleasing support from the photosensitive resin layer having such a hightack. For this reason, a releasing support having good releasecharacteristics, for example, a synthetic resin film or a waxed paper,is ordinarily used. Even in case such a releasing support having goodrelease characteristics is used, however, various troubles tend to occurwhen the releasing support is removed from the photosensitive resinlayer. For example, the photosensitive resin layer is peeled offtogether with the releasing support from the conductive metal layer, orpinholes are liable to be formed in the photosensitive resin layer.Further, adhesion of dusts are caused due to static charge generated bythe removal of the releasing support. Therefore, the abovementionedmethod cannot be commercially applicable to the production of printedcircuit boards having good through-holes.

All of the foregoing disadvantages accompanying the conventional methodsfor the production of printed circuit boards can be eliminated accordingto this invention. Differently stated, according to this invention,printed circuit boards having good conductive metal layers on the innerwall surfaces of the through-holes can be prepared very simple whileomitting the step of removing the releasing support from thephotosensitive resin layer.

Accordingly, in a further aspect of this invention, there is provided aprocess for the production of a printed circuit board, which comprisesthe steps of:

(1) applying, to the surfaces of both sides of an insulating substratehaving on its both sides conductive metal layers and havingthrough-holes with their respective inner wall surfaces coverd withconductive metal layers, the surface of a photosensitive compositionlayer having adherence to the substrate to cover and close at least bothopenings of each of the through-holes with the photosensitivecomposition layer, while the other surface of the photosensitivecomposition layer has adhered to a substantially transparent filmsupport which is soluble or dispersible in a developer consistingessentially of a liquid capable of substantially dissolving ordispersing therein the areas of the layers other than those havingpolymeric images produced by imagewise exposure in the step (2) belowand capable of transmitting actinic rays, the application of the surfaceof the photosensitive composition layer to the surface of the substratebeing effected after stripping of a protective film in case theprotective film has been provided on the surface of the photosensitivecomposition layer remote from the film support;

(2) exposing the photosensitive composition layers on both sides of thesubstrate, imagewise, to actinic radiation through the respective filmsupports to form in the layers polymeric images covering at least bothopenings of each of the through-holes;

(3) washing away with the developer the film supports and the areas ofthe layers other than those having the polymeric images to formpolymeric image patterns on both sides of the substrate; and

(4) etching the conductive metal layers in the areas other than theareas of the polymeric image patterns as masking resists.

In the above-mentioned method, either a negative working photosensitivecomposition capable of polymerizing by exposure or a positive workingphotosensitive composition capable of degrading by exposure may be usedfor the photosensitive composition layer. As the negative workingphotosensitive composition, there can be used the aforementionedcompositions comprising an organic polymer binder, an ethylenicallyunsaturated compound and a sensitizing agent. As the positive workingphotosensitive composition, there can be preferably used theaforementioned compositions comprising an o-quinone diazide.

Liquid developers capable of dissolving or dispersing therein thenon-imaged areas of the photosensitive composition layer and the supportlayer, such as exemplified hereinbefore, can be used as the developerfor the manufacture of through-hole printed circuit boards.

Other objects, features and advantages of the method according to theinstant aspect of this invention will be better understood from thedescription taken in connection with the accompanying drawings in which:

FIGS. 1 to 3 and 5 to 9 are diagrammatic sectional views illustrating byway of example the successive steps of manufacturing a printed circuitboard according to the instant aspect of this invention; and

FIG. 4 is a diagramatic sectional view of one form of a photosensitiveelement to be used in practicing the process of this invention.

Referring now to FIGS. 1 to 9, the method of the producing a printedcircuit board by the use of a negative working photosensitive elementwill be explained as one embodiment of the instant aspect of thisinvention.

As is shown in FIG. 1, both surfaces of an insulating substrate 1 madeof, for example, a phenolic or epoxy resin are clad with copper foils toform thin copper layers 2 and 3. Then, as is shown in FIG. 2,through-holes 4 and 5 are formed at predetermined portions by drillingor punching. In FIG. 3, the inner wall surfaces of the through-holes 4and 5 are subjected to electroless plating to form an initial thindeposit of copper and subsequently, to electro-plating to formthrough-hole conductor layers 6 and 7 of the desired thickness, whichare thin copper layers. If a photosensitive element has a protectivefilm 10 made of polyethylene or the like as is shown in FIG. 4, theprotective film is peeled off. The surfaces of photopolymerizable layers9 and 12, which are remote from film supports 8 and 11, are applied toboth surfaces of the copper-clad insulating substrate under applicationof an appropriate pressure at about 0° to about 160° C. to form alaminate board, whereby at least both openings of each of thethrough-holes 4 and 5 whose inner wall surfaces have respectively thethrough-hole conductor layers 6 and 7 are covered with thephotopolymerizable layers 9 and 12 as is shown in FIG. 5. The thicknessof the photopolymerizable layers 9 and 12 is preferably 0.5 to 100μ,more preferably 5 to 70μ, though it is not particularly critical. Then,as is shown in FIG. 6, the photopolymerizable layers are imagewiseexposed through negative films 13 and 14 to actinic radiation to form inthe photopolymerizable layers polymeric images insoluble in the liquiddeveloper. Then, as is shown in FIG. 7, the film supports 8 and 11 andthe unexposed non-imaged areas of the layers are dissolved away ordispersed away and removed using a liquid developer by means of anadequate development method such as a spray development method. In themethod according to the instant aspect of this invention, it isindispensable that at least both openings of each of the through-holes 4and 5 should be completely covered with photopolymerized areas 9a, 9band 12a insoluble in the liquid developer. The development may beeffected in sequence or simultaneously for each of both sides of thelaminate board. Subsequently, the resulting board is dipped in anetching solution containing ferric chloride or the like to effectetching of the thin copper layers 2 and 3. The portions of the thincopper layers other than those covered with the insolublephotopolymerized areas 9a, 9b, 12a, etc. of the polymeric images asmasking resists are etched away with the etching solution to formdesired conductor patterns as is shown in FIG. 8, followed by washingwith water. Then, as is shown in FIG. 9, the insoluble photopolymerizedareas 9a, 9b, 12a, etc. of the polymeric images are removed by dippingin methylene chloride or the like, followed by washing. According toneed, the thin copper layers 2 and 3 and the through-hole conductorlayers 6 and 7 are plated with gold or solder. Thus, there is obtained aprinted circuit board having excellent quality through-hole conductorlayers 6 and 7.

As will be apparent from the foregoing illustration, when a printedcircuit board is produced according to the method of this invention, thestep of removing the releasing support is not needed, leading to thesimplification of the manufacturing process. Further, such problemsaccompanying the conventional method as the peeling-off of aphotosensitive resin layer from the conductive metal layer, theformation of pinholes and the adhesion of dusts by static charge at thestep of stripping a releasing support need not be cared for at all inthe method of this invention. Accordingly, a printed circuit boardhaving through-holes with their respective inner walls covered byexcellent conductor layers can be mass-produced, without giving poorquality products, with commercial advantages.

Further, it is noted that the photosensitive element according to thisinvention may advantageously be manufactured in the form of alongitudinally elongated strip that can be wound into a roll, from theviewpoint of handling, storage, etc.

The following Examples illustrate this invention in more detail, but arenot to be construed as limiting the scope thereof.

In Examples, "resolution" is evaluated as follows. According to theprocess of this invention, a plurality of polymeric images are producedusing a photosensitive element and a plurality of mask films whichdiffer in the line width of the image composed of transparent lineshaving a given width and opaque lines having the same width as that ofthe transparent lines. Each polymeric image is visually observed througha microscope to determine whether or not the polymeric image hasrecognizable lines. The minimum line width among the line widths of theimages of those mask films which can give a polymeric image havingrecognizable lines is defined as the "resolution" of the photosensitiveelement.

The viscosity average molecular weight (Mv) shown in this specificationis calculated from the intrinsic viscosity [η] at 25° C. of a solutionof a polymer material in a solvent, using the following equation. Theintrinsic viscosity is examined using Ostwald's viscosmeter.

    [η]=KM.sup.-α.sub.v

(wherein K and α are constants inherent of the kind of a polymericmaterial).

For example, with respect to polymethyl methacrylate and polystyrene,solvents to be used and constants K and α are listed as follows.

    ______________________________________                                                       Solvent K          α                                     ______________________________________                                        Polymethyl methacrylate                                                                        chloroform                                                                              4.85 × 10.sup.-6                                                                   0.80                                    Polystyrene      benzene   1.0  × 10.sup.-4                                                                   0.74                                    ______________________________________                                    

The viscosity average molecular weight (Mv) is substantially the same asthe weight average molecular weight (Mw).

In Examples, a film support is often referred to simple as "support".

EXAMPLE 1

A solution for a photopolymerizable layer was prepared of the followingingredients:

    ______________________________________                                        Methyl methacrylate/methacrylic                                               acid copolymer (molar ratio =                                                 90/10; --M.sub.v = 120,000)                                                                            40 g                                                 Trimethylolpropane triacrylate                                                                         15 g                                                 2-Ethylanthraquinone     0.5 g                                                Methyl violet (C. I. 42535)                                                                            0.1 g                                                p-Methoxyphenol          0.15 g                                               Methyl ethyl ketone      140 g                                                ______________________________________                                    

The so prepared solution was coated onto a 25μ-thick polyethyleneterephthalate film and dried at 80° C. for 5 minutes to form aphotopolymerizable layer having a dry thickness of 12μ. A 20μ-thickbiaxially oriented polystyrene film Styrofilm (registered trademark of aproduct manufactured and sold by Asahi-Dow Limited, Japan) as a supportwas laminated onto the photopolymerizable layer using a pressure rollerto form a photosensitive element.

A copper-clad epoxy resin-fiber glass substrate was degreased withtrichloroethylene, dipped for 30 seconds in a 10% by weight aqueoussolution of hydrochloric acid, washed with water, coarsened by a surfaceabrasion machine [a roll Scotchbrite (registered trademark) 7VF(manufactured and sold by Minesota Mining and Manufacturing Company,U.S.A.) was used], washed with water and then dried.

The polyethylene terephthalate film as the protective film of thephotosensitive element was stripped, and the photopolymerizable layerwith its support was laminated through nip rolls onto the so treatedcopper-clad substrate heated at 90° C. to form a laminate board. Thelamination pressure was 2.0 Kg/cm².G and the lamination speed was 1.0m/min. The adhesion between the biaxially oriented polystyrene film asthe support and the photopolymerizable layer was very large, andtherefore when it was tried to separate them forcibly from each other,the film support was broken or peeling-off took place between the coppersurface and the photopolymerizable layer.

The photopolymerizable layer of the so formed laminate board was exposedfor 45 seconds through a negative image to actinic rays from a 3 KW highpressure mercury lamp (manufactured by Ushio Electric Inc., Japan)located at a distance of 50 cm from the surface of the support. Then,1,1,1-trichloroethane was jetted for 60 seconds to the laminate boardfrom a spray nozzle to dissolve away and remove the support film and theunexposed areas of the photopolymerizable layer, whereby a resist imagewas obtained. The resolution was examined and clear lines of 25μ inwidth were observed. A 50° C., 45° Baume ferric chloride solution wasjetted to the laminate board by a nozzle type etching machine to removecopper at the areas unprotected by the resist image. By this etchingtreatment, the resist image did not undergo any change and remainedfirmly adhered to the copper-clad substrate. The etched laminate boardwas then washed with water and dried, and the resist was removed usingmethylene chloride. A copper pattern having a line width of 25μ wasclearly obtained.

EXAMPLE 2

A solution for a photopolymerizable layer was prepared of the followingingredients:

    ______________________________________                                        Styrene/acrylonitrile copolymer                                               (molar ratio = 85/15; --M.sub.v = 150,000)                                                              50 g                                                Pentaerythritol triacrylate                                                                             15 g                                                2-methylanthraquinone     0.5 g                                               Victoria Blue (C.I. 42563)                                                                              0.2 g                                               Methyl ethyl ketone       280 g                                               ______________________________________                                    

The so prepared solution was coated onto a 50μ-thick polypropylene filmto form a photopolymerizable layer having a dry thickness of 15μ. Thisphotopolymerizable layer was laminated onto a 15μ-thick biaxiallyoriented polystyrene film. Lamination onto a substrate, exposure anddevelopment were conducted in the same manner as described in Example 1.The resolution was 30μ. The resist image did not undergo any change bythe etching treatment, and a good pattern was obtained when the resistwas removed.

EXAMPLE 3

A solution for a photopolymerizable layer was prepared of the followingingredients:

    ______________________________________                                        Chlorinated polyethylene [Super                                               Chlon (registered trademark) 907LTA                                           manufactured and sold by Sanyo-Kokusaku                                       Pulp Co., Ltd., Japan]     21 g                                               Polymethyl methacrylate [Delpowder                                            (registered trademark) 80N manufactured                                       and sold by Asahi Kasei Kogyo K.K.,                                           Japan]                     9 g                                                Trimethylolpropane triacrylate                                                                           20 g                                               Benzophenone               0.5 g                                              Michler's ketone           0.25 g                                             Malachite Green (oxalate)  0.1 g                                              Methyl ethyl ketone        150 g                                              ______________________________________                                    

The solution was coated onto a 50μ-thick polypropylene film to form aphotopolymerizable layer having a dry thickness of 10μ. Then, thephotopolymerizable layer was laminated onto a 20μ-thick biaxiallyoriented polymethyl methacrylate film as a support. The polypropylenefilm was stripped and the photopolymerizable layer with its support waslaminated through nip rolls onto a copper-clad epoxy resin substrateheated at 100° C. The lamination pressure was 4.0 Kg/cm².G and thelamination speed was 1.5 m/min. Exposure and development were carriedout under the same conditions as adopted in Example 1. The resolutionwas 20μ. The resist image was stable even after the etching treatment,and when the resist was removed, a good pattern was obtained.

EXAMPLE 4

The solution prepared in Example 1 was coated onto a 25μ-thickpolyethylene terephthalate film to form a photopolymerizable layerhaving a dry thickness of 10μ, and the photopolymerizable layer waslaminated onto a 20μ-thick unoriented polycarbonate film as a support toform a photosensitive element. Then, the polyethylene terephthalate filmwas stripped, and the photopolymerizable layer with its support waslaminated with pressing onto a copper-clad epoxy resin substrate heatedat 100° C. to form a laminate board. The lamination pressure was 2.5Kg/cm².G and the lamination time was 30 seconds. Then, thephotopolymerizable layer of the laminate board was exposed for 30seconds through a negative image to actinic rays from a 2 KW super-highpressure mercury lamp (manufactured by Ork Manufacturing Co., Ltd.,Japan) located at a distance of 50 cm from the surface of the support.Tetrahydrofuran was jetted for 45 seconds to the laminate board from aspray nozzle to dissolve away and remove the film support and theunexposed areas of the photopolymerizable layer and obtain a resistimage. The resolution was examined, and clear lines of 30μ in width wereobserved. The laminate board was then etched by a spray nozzle typeetching machine under the same conditions as adopted in Example 1. Theresist image did not undergo any change and it remained adhered firmlyto the copper-clad substrate. The laminate board was washed with waterand dried, and the resist was removed using methylene chloride to obtaina good copper pattern consisting of lines of 30μ in width.

EXAMPLE 5

A solution for a photopolymerizable layer was prepared in the samemanner as described in Example 3, and the solution was coated onto a50μ-thick polypropylene film to form a photopolymerizable layer having adry thickness of 15μ. The coated film was laminated onto a 20μ-thickbiaxially oriented polyvinyl chloride film as a support to obtain aphotosensitive element. The polypropylene film was stripped and thephotopolymerizable layer with its support was laminated onto acopper-clad epoxy resin substrate heated at 100° C. Exposure anddevelopment were carried out under the same conditions as adopted inExample 4 to obtain a resist image. When the resolution was examined, itwas found to be 30μ. Even after the etching treatment, the resist imagewas stable, and when the resist was removed, a good pattern wasobtained.

EXAMPLE 6

A solution for a photopolymerizable layer was prepared of the followingingredients:

    ______________________________________                                        Cellulose acetate butyrate                                                                             30 g                                                 (--Mv = 60,000)                                                               Trimethylolpropane triacrylate                                                                         10 g                                                 2-Methylanthraquinone    0.5 g                                                Victoria Blue (C.I. 42563)                                                                             0.2 g                                                Methyl ethyl ketone      160 g                                                ______________________________________                                    

The so prepared solution was coated onto a 25μ-thick polyethyleneterephthalate film to form a photopolymerizable layer having a drythickness of 10μ. A 15μ-thick unoriented cellulose diacetate film waslaminated onto the surface of the photopolymerizable layer using apressure roller to obtain a photosensitive element. The polyethyleneterephthalate film as the protective film of the photosensitive elementwas stripped, and the photopolymerizable layer was laminated onto acopper-clad phenolic resin substrate with pressing at room temperatureto form a laminate board. In substantially the same manner as describedin Example 1, the photopolymerizable layer of the laminate board wasexposed to actinic rays and development was effected with acetone toform a resist image. This resist image was clear and sufficientlyresisted an etching treatment by the use of a ferric chloride solution.When the resist was removed after the etching treatment, a good patternwas obtained.

COMPARATIVE EXAMPLE 1

In the same manner as described in Example 1, a photopolymerizable layerhaving a dry thickness of 12μ was formed on a 25μ-thick polyethyleneterephthalate film as a support. In substantially the same manner asdescribed in Example 1, the photopolymerizable layer with its supportwas laminated with pressing onto a copper-clad expoxy resin substrateheated at 90° C. and exposure to actinic rays was effected. When thepolyethylene terephthalate film was stripped, part of thephotopolymerizable layer remained adhered to the copper-clad substrateand the other part of the photopolymerizable layer remained adhered tothe polyethylene terephthalate film. Thus, the photopolymerizable layerwas destroyed and the image was in disorder.

COMPARATIVE EXAMPLE 2

A photopolymerizable layer formed on a 50μ-thick polypropylene film as asupport in the same manner as described in Example 3 was laminated ontoa copper-clad epoxy resin substrate heated at 100° C. in substantiallythe same manner as described in Example 3 to form a laminate board.Exposure to actinic ray was effected in substantially the same manner asdescribed in Example 1. When the polypropylene film as the support wasstripped, the photopolymerizable layer was destroyed and remainedadhered to both the film support and the copper surface. Accordingly, itwas practically useless to subject the resulting laminate board todevelopment.

EXAMPLE 7

A solution for a photopolymerizable layer was prepared in substantiallythe same manner as described in Example 1 except that the amount of2-ethylantraquinone as a photopolymerizable initiator was 1.5 g insteadof 0.5 g. This solution was referred to as a solution A. The samesolution as prepared in Example 1 was referred to as a solution B.

The solution A was coated onto a 25μ-thick polyethylene terephthalatefilm and dried to form a layer A having a dry thickness of 12μ, and thesolution B was coated onto the layer A and dried to form a layer Bhaving a dry thickness of 12μ. A photopolymerizable layer having a totalthickness of 24μ was obtained. The photopolymerizable layer waslaminated onto a 20μ-thick biaxially oriented polystyrene film.

In substantially the same manner as described in Example 1, laminationonto a copper plate, imagewise exposure and development was carried outto form a resist image on the copper substrate.

The so obtained resist image had substantially vertical lateral faces.It was not observed that the degree of polymerization in the layer A waslower than that in the layer B due to the scattering of actinic rays.

EXAMPLE 8

A solution for a photopolymerizable layer was prepared in substantiallythe same manner as described in Example 1 except that the amount ofp-methoxyphenol as a polymerization inhibitor was 0.03 g instead of 0.15g. This solution was referred to as a solution C. The same solution asprepared in Example 1 was referred to as a solution D.

The solution C was coated onto a 25μ-thick polyethylene terephthalatefilm and dried to form a layer C having a dry thickness 10μ, and thesolution D was coated onto the layer C and dried to form a layer Dhaving a dry thickness of 10μ. A photopolymerizable layer having a totalthickness of 20μ was obtained. The photopolymerizable layer waslaminated onto a 20μ-thick biaxially oriented polystyrene film.

In substantially the same manner as described in Example 1, laminationonto a copper substrate, imagewise exposure and development were carriedout to form a resist image on the copper substrate.

The cross-sections of the so obtained resist image was observed. Theresist image had substantially vertical lateral faces and goodcross-sections in a substantially rectangular shape. This effect was dueto substantially uniform polymerization attained by providing in thephotopolymerizable layer the layer C containing the smaller amount ofthe polymerization inhibiter in order to increase the photosensitivityof the layer C.

EXAMPLE 9

0.6 g of benzimidazole was added to the same solution as prepared inExample 1. The resulting solution was coated onto a 25μ-thickpolyethylene terephthalate film and dried to form a photopolymerizablelayer having a dry thickness of 25μ. The photopolymerizable layer waslaminated onto a 20μ-thick biaxially oriented polystyrene film as asupport to obtain a photosensitive element.

The polyethylene terephthalate film was stripped and the baredphotopolymerizable layer was laminated onto a copper substrate in thesame manner as described in Example 1 to form a laminate board. Exposureto actinic rays was effected in substantially the same manner asdescribed in Example 1 except that a negative film was not used. Also,the same photopolymerizable layer with its support as prepared inExample 1 was laminated onto a copper substrate in the same manner asdescribed in Example 1 to form a laminate board and exposed to actinicrays in the same manner as described above. 1,1,1-Trichloroethane wasjetted to each laminate board in the same manner as described in Example1 to remove the support. An epoxy resin adhesive Araldite (registeredtrademark) standard (manufactured and sold by Ciba-Geigy Co., Ltd.,Switzerland) was applied onto the surface of a bared photopolymerizedlayer of each resulting laminate board, and a copper substrate waslaminated onto the adhesive layer to form a sample laminate board.

The shear stress between the photopolymerized layer and the coppersubstrate of each sample laminate board was examined in accordance withASTM-D1002-64. The shear stress between the photopolymerized layercontaining benzimidazole and the copper substrate was 30 Kg/cm², whilethe shear stress between the photopolymerized layer containing nobenzimidazole and the copper substrate was 18 Kg/cm². Thus, it wasconfirmed that benzimidazole exerted a marked effect with respect to theadhesion between the photopolymerized layer and the copper substrate.

EXAMPLE 10

A solution for a photosensitive layer was prepared of the followingingredients:

    ______________________________________                                        Methyl methacrylate/methacrylic acid copolymer                                (molar ratio = 90/10 ; --Mv = 90,000)                                                                     5 g                                               Cresol novalak resin Sumiliteresin                                            (registered trademark of a product                                            manufactured and sold by Sumitomo                                             Bakelite Co., Ltd., Japan) 15 g                                               2-(Naphthoquinone-1,2-diazide-5-                                              sulfonyloxy)-7-oxynaphthalene                                                                            10 g                                               Victoria Blue (C.I. 42563)   0.3 g                                            Dioxane                    40 g                                               Ethylene dichloride        30 g                                               ______________________________________                                    

The so prepared solution was coated onto a 20μ-thick unorientedpolyvinyl alcohol film as a support and dried to form a photosensitivelayer having a dry thickness of 20μ. The photosensitive layer with itssupport was laminated with pressing onto a copper-clad epoxy resinsubstrate heated at 80° C. to form a laminate board. The laminationpressure was 2.0 Kg/cm².G and the lamination time was 30 seconds. Thephotosensitive layer was exposed for 30 seconds through a positive filmto actinic rays from the same high pressure mercury lamp as used inExample 1, which was located at a distance of 50 cm from the surface ofthe support. Subsequently, a liquid developer composed of an aqueous0.5% by weight sodium hydroxide solution was jetted for 2 minutes to thelaminate board from a spray nozzle to dissolve away and remove thesupport film and the exposed areas of the photosensitive layer. Theobtained image has clearly defined lines of 30μ in width.

EXAMPLE 11

A solution for a photopolymerizable layer was prepared of the followingingredients:

    ______________________________________                                        Methyl methacrylate/acrylic acid copolymer                                    (molar ratio = 95/5 ; --Mv = 150,000)                                                                  50 g                                                 Tetraethylene glycol diacrylate                                                                        40 g                                                 Methyl Violet (C.I. 42535)                                                                               0.2 g                                              2-Ethylanthraquinone      4 g                                                 Methyl ethyl ketone      300 g                                                ______________________________________                                    

The so prepared solution was coated onto a 40μ-thick polyethylene filmand dried at 80° C. for 2 minutes to form a photopolymerizable layerhaving a dry thickness of 30μ. A 25μ-thick unoriented polyvinyl alcoholfilm as a support was laminated onto the photopolymerizable layer underapplication of pressure to form a photosensitive element.

The polyethylene film which was a protective film of the photosensitiveelement was stripped. Then, the photopolymerizable layer with itssupport was laminated onto the cleansed surface of a 1 mm-thick copperplate heated at 80° C., which copper plate had a protective coating onthe other surface thereof. Subsequently, the photopolymerizable layerwas exposed for 40 seconds to actinic rays from the same high pressuremercury lamp as used in Example 1, which was located at a distance of 50cm from the surface of the support. Development was effected using asolution composed of 0.2% by weight of sodium hydroxide, 10% by weightof isopropanol and 89.8% by weight of water. The polyvinyl alcohol filmas the support and the unexposed areas of the photopolymerizable layerwere swollen, dispersed and removed to obtain a desired resist image.

The same ferric chloride solution as used in Example 1 was jetted for 2minutes to the resist image-bearing copper plate to effect etching.After water-washing and drying, the resist was removed using methylenechloride. The resulting copper plate was cut into a circular form toform a decorative article.

EXAMPLE 12

A double-side copper-clad epoxy substrate was subjected to drilling toform through-holes having a diameter of 1.5 mm at the predeterminedportions of the substrate, followed by deburring. The substrate wascatalyzed, at the inner wall surfaces of through-holes, by an ordinarymethod using a palladium chloride solution, and subjected to electrolessplating and ellectroplating to effect copper plating on the inner wallsurfaces of the through-holes. A substrate having through-holes linedwith an about 20μ-thick copper conductor layer was obtained.

The so obtained substrate was heated to 90° C. The polyethyleneterephthalate films were removed from sections of two pieces of the samephotosensitive element as prepared in Example 1. The baredphotopolymerizable layers with their supports were laminated onto bothsurfaces of the heated substrate through nip rolls to form a laminateboard. The lamination pressure was 2.0 Kg/cm².G and the lamination speedwas 1.0 m/min. The laminate board was exposed from both sides thereoffor 45 seconds through negative films to actinic rays from the samesuper-high pressure mercury lamps as used in Example 4, which werelocated at a distance of 50 cm from each surface of the laminate board,to produce polymeric images covering both openings of eachthrough-holes. 1,1,1-Trichloroethane was jetted for 60 seconds to thellaminate board from a spray nozzle to dissolve away and remove thesupport films and the un-exposed areas of the photopolymerizable layer,whereby resist images covering both the openings of each through-holeswere obtained. A 50° C., 45° Baume ferric chloride solution was jettedto the laminate board by a spray type etching machine to remove copperat the areas unprotected by the resist images. At the etching step, theresist images did not undergo any change and effectively protected thethrough-hole portions. After water-washing and drying, the resists wereremoved using methylene chloride to obtain an excellent through-holeprinted circuit board. The about 20μ-thick copper conductor layersplated on the inner wall surfaces of the through-holes did not undergoany change.

What is claimed is:
 1. A process for producing an image, which comprisesthe steps of:(1) applying to the surface of a substrate the surface of aphotosensitive composition layer having adherence to the substrate,while the other surface of the photosensitive composition layer haslaminated to it a substantially transparent oriented film support whichis soluble or dispersible in a developer consisting essentially of aliquid capable of substantially dissolving or dispersing therein theareas of the layer other than those having a polymeric image produced byimagewise exposure in the step (2) below and capable of transmittingactinic rays, the application of the surface of the photosensitivecomposition layer to the surface of the substrate being effected afterstripping of a protective film in case the protective film has beenprovided on the surface of the photosensitive composition layer remotefrom the film support; (2) exposing the photosensitive compositionlayer, imagewise, to actinic radiation to form a polymeric image in thelayer; and (3) washing away with the developer the film support and theareas of the layer other than those having the polymeric image to forman image of a polymeric material on the substrate.
 2. A processaccording to claim 1, wherein the photosensitive composition of saidphotosensitive composition layer is a photopolymerizable composition. 3.A process according to claim 2, wherein said photopolymerizablecomposition comprises an organic polymer binder, an ethylenicallyunsaturated compound and a photopolymerization initiator.
 4. A processaccording to claim 3, wherein said organic polymer binder is ahomopolymer or copolymer of methyl methacrylate and the ethylenicallyunsaturated compound is an acrylic polyfunctional monomer.
 5. A processaccording to claim 1, wherein the photosensitive composition of saidphotosensitive composition layer is a photodegradable composition.
 6. Aprocess according to claim 5, wherein said photodegradable compositionis a composition containing an o-quinone diazide and said film supportis of a water-soluble polymer.
 7. A method according to claim 6, whereinsaid film support is of polyvinyl alcohol, polyvinyl pyrrolidone orcellulose acetate succinate.
 8. A process according to claim 2, whereinsaid film support is an oriented film support made of a member selectedfrom the group consisting of styrene homopolymer and copolymers, methylmethacrylate homopolymer and copolymers, polyvinyl chloride, polyvinylacetate, vinyl chloride-vinyl acetate copolymers, polycarbonates andmixtures thereof.
 9. A process according to claim 2, wherein saiddeveloper is a member selected from the group consisting of ketones,esters, alcohols, chlorinated hydrocarbons, aromatic hydrocarbons andmixtures thereof.
 10. A process according to claim 9, wherein saiddeveloper is a member selected from the group consisting of methyl ethylketone, ethyl acetate, trichloroethylene, 1,1,1-trichloroethane andmixtures thereof.
 11. A process according to claim 4, wherein saidphotopolymerizable composition is a composition comprising polymethylmethacrylate as the organic polymer binder, trimethylolpropanetriacrylate as the ethylenically unsaturated compound and aphotopolymerization initiator; said oriented film support is made ofpolystyrene or polymethyl methacrylate; and said developer is a memberselected from the group consisting of methyl ethyl ketone, ethylacetate, trichloroethylene, 1,1,1-trichloroethane and mixtures thereof.12. A process according to claim 1, wherein said substrate is a metalplate made of a member selected from the group consisting of copper,aluminum, iron, zinc, brass, silver, gold and stainless steel.
 13. Aprocess according to claim 1, wherein said substrate is a laminate boardhaving in its surface portion or portions a layer or layers made of asubstance etchable with an etching solution.
 14. A process according toclaim 13, wherein said etchable substance is a metal.
 15. A processaccording to claim 14, wherein said metal is a member selected from thegroup consisting of copper and aluminum.
 16. A process according toclaim 1, wherein said substrate is of a member selected from the groupconsisting of glass and stone.
 17. A process according to claim 1,wherein at the step (1), the application of the surface of thephotosensitive composition layer to the surface of the substrate isconducted keeping the temperature of the surface of said substrateand/or the surface of said photosensitive composition layer remote fromthe film support at about 0° to about 160° C.
 18. A process according toclaim 17, wherein said temperature is about 10° to about 120° C.
 19. Aprocess according to claim 1, wherein at the step (1), the applicationof the surface of the photosensitive composition layer to the surface ofthe substrate is conducted with applying a pressure of about 0.1 toabout 20 kg/cm².G between said substrate and said photosensitivecomposition layer.
 20. A process according to claim 19, wherein saidpressure is about 0.5 to about 5.0 kg/cm².G.
 21. A method of producing aprinted circuit board in accordance with the process of claim 1, whereinsaid substrate is an insulating board having, at least on one sidethereof, a conductive metal layer, and which comprises, followingformation of the image of the polymeric material, the step of:(4)etching the conductive metal layer in the areas other than the areas ofthe image of the polymeric material as a masking resist.
 22. A methodaccording to claim 21, wherein said substrate is an insulating boardhaving on its both sides a conductive metal layer and is provided withthrough-holes, and which comprises, following etching, the steps of:(5)covering the entire surfaces of both sides with a resist except portionscorresponding to the through-holes; and (6) plating an electrolessdeposit of a conductive metal on the inner wall surfaces of thethrough-holes, optionally followed by electro-deposition of a conductivemetal on said electroless deposit.
 23. A method according to claim 21,wherein in the step (1) said substrate is an insulating board having onits both sides conductive metal layers and is provided withthrough-holes having their respective inner wall surfaces covered with aconductive metal layer, and the application of the surface of thephotosensitive composition layer is conducted onto the surfaces of bothsides of the substrate to cover and close at least both openings of eachof the through-holes; and in the step (2) the exposure is conducted withrespect to the photosensitive composition layers on both sides of thesubstrate to form in the layers polymeric images covering at least bothopenings of each of the through-holes.
 24. A method of producing aprinted circuit board in accordance with the process of claim 1, whereinsaid substrate is a bare insulating board, and which comprises,following formation of the image of the polymeric material, the stepof:(4) plating an electroless deposit of a conductive metal on the areasother than the areas of the image of the polymeric material, optionallyfollowed by electro-deposition of a conductive metal on said electrolessdeposit.
 25. A method of producing a printed circuit board in accordancewith the process of claim 1, wherein said substrate is a bare insulatingboard having through-holes and the entire surface of the substrateincluding the inner walls of the through-holes has an initial thinconductive metal electrolessly deposited thereon, and which comprises,following formation of the image of the polymeric material, the stepsof:(4) applying additional metal plating by electro-deposition on saidinitial thin conductive metal to build up the conductor portions of thecircuit to a desired thickness; and (5) removing the photoresist fromthe non-circuit portions and etching away the initial thin electrolessmetal deposit therefrom.
 26. A photosensitive process according to claim1, wherein the thickness of said transparent oriented film support is 5to 100μ.
 27. A process according to claim 26, wherein said thickness is10 to 50μ.